Wednesday Late Afternoon Update:
With widespread temperatures in the low to mid 40s, scattered showers, and road temperatures in the 40s, we don't think this system will be much of an issue for the D.C. Metro or even points north and west at this time. There have been a few reports of flurries or snow showers at the onset of precipitation in the Shenandoah Valley, but otherwise, it's been all rain out there.
The main energy is still expected to push through the area later this evening between 5pm and 8pm, and showers will continue to be possible. There is still the slight chance for a few light snow showers, mainly north and west of the D.C. Metro closer western Loudoun and Frederick Counties and points west. Higher elevations will have a much better shot of seeing light snow. Here is a look at the 4km NAM model for 8pm tonight, showing the potential for a few flakes west of the Blue Ridge.
- 4km NAM forecast for 8pm this evening (WeatherBELL Models)
As far as the D.C. Metro is concerned, a few flurries may be possible around 8 or 9pm tonight, but we wouldn't be entirely surprised if precipitation never changes back to snow before ending.
Previous Discussion Below
Wednesday Morning Update (Adam Caskey): The latest guidance is not looking good for snow lovers. As of now, it looks as though temperatures will be a little too warm for much snow to fall across the abc7 viewing area later today. That said, minor accumulations are still expected north and west of Washington, D.C. As for the metro area, the most likely scenario is a light frosting of snow on some grassy areas by late in the evening. A breakdown of the snow odds for the D.C. metro is shown here:
- Metro Area Snow Odds
I think our Microcast (shown below) has a pretty good handle on the situation, but it may be underestimating snow amounts in the hills west and northwest of Washington. As usual, higher elevations will have more snowfall potential, so 1-2" is possible in the hills just west and northwest of D.C. including but not limited to parts of Loudoun, Fauquier, Frederick and Washington Counties. We'll have another update close to noon as the rain begins, so check back to see if anything changes.
- Microcast Model
An area of low pressure will move into the area on Wednesday bringing with it the chance for rain as well as the chance for snow. With temperatures in the 50s today ahead of the system, we think much of the area will not see much in the way of accumulation. Some areas may receive a couple of inches, with the highest potential for accumulating snow well north and west of the D.C. Metro.
- HPC Probability of >= 1" Snow
Above is a look at the latest probabilities for greater than or equal to one inch of snow from the Hydrometeorological Prediction Center which is fairly close to what we are thinking. This gives about a 40-50% chance for an inch of snow in the D.C. area, though we think that would mainly be on the grassy surfaces given the rain at the onset of precipitation and the warmer ground temperatures. There is a much higher likelihood (80-90%) of accumulating snow north and west of D.C., particularly in the higher elevations towards the Blue Ridge and even areas such as northern Montgomery County.
Our current thought is that precipitation will begin in the form of light rain or sprinkles tomorrow morning during the latter part of the commute (9-10am). More steady rain should continue for the D.C. Metro and points south and east through the afternoon hours, with the potential of a couple tenths of an inch. Rain will changeover to snow by the afternoon hours north and west of D.C., where colder air will filter in as the low passes just south of the area. We think this will mainly occur along and west of the Blue Ridge first, but then also changeover in Frederick, MD and northern Loudoun and Montgomery counties as well.
- 4km NAM for 7pm Wednesday evening (WeatherBELL Models)
The D.C. Metro and points south and east will have to wait the longest for the changeover, which appears like it will occur during the evening rush hour. The timing looks like it would occur anywhere from 4-6pm for the changeover to snow, but a few models hold off even longer closer to 8-9pm tomorrow evening. The model depiction above is the 4km NAM which shows the changeover occuring closer to 7pm in the D.C. Metro.
Ok, how much are we looking at?
Yes, enough of the timing, everyone wants to know how much to expect. For the D.C. Metro and points south and east, our thoughts are for a half of an inch or less. Some of the higher spots in northern Montgomery County may get a couple inches (1-2") and spots along the Blue Ridge a little more (2-4"). I think as of now the best chance for snow will be closer to Hagerstown, Martinsburg and points northwest for the Mountains. These ares have the chance for 2-4" with places in the mountains up to 5".
- HPC 1-2 Day Precipitation Forecast
As far as precipitation is concerned, there is about a half of an inch of precipitation possible with this system. Our snow ratios should be close to 10 to 1, meaning for an inch of rain, it would equate to 10 inches of snow. So the most snow the majority of the area would look at would be 5 inches given that half an inch of precipitation. I do see an issue with getting that much snow, however, given the warm temperatures today, the warm surface temperatures and the fact it may need to snow for a while before accumulations occur.
Main roadways should be ok, as we are sure once again they will be treated, but some side roads will be sure to have some slick spots. However, if a heavy band of snow develops, which is quite possible NW of D.C., a few main roadways could have accumulating snow. A few schools may be let out early in areas northwest of D.C., and travel will be affected by wet roads and poor visibility, not to mention rain, for tomorrow afternoon and evening, so keep that in mind.